From patchwork Thu Jan 12 11:26:08 2017 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Dave Martin X-Patchwork-Id: 18869 Received: (qmail 73311 invoked by alias); 12 Jan 2017 11:26:43 -0000 Mailing-List: contact libc-alpha-help@sourceware.org; run by ezmlm Precedence: bulk List-Id: List-Unsubscribe: List-Subscribe: List-Archive: List-Post: List-Help: , Sender: libc-alpha-owner@sourceware.org Delivered-To: mailing list libc-alpha@sourceware.org Received: (qmail 73001 invoked by uid 89); 12 Jan 2017 11:26:41 -0000 Authentication-Results: sourceware.org; auth=none X-Virus-Found: No X-Spam-SWARE-Status: No, score=-2.3 required=5.0 tests=BAYES_00, RP_MATCHES_RCVD, SPF_PASS, UNWANTED_LANGUAGE_BODY autolearn=ham version=3.3.2 spammy=private_data, sk:THREAD_, ENOMEM, enomem X-Spam-User: qpsmtpd, 2 recipients X-HELO: foss.arm.com From: Dave Martin To: linux-arm-kernel@lists.infradead.org Cc: Ard Biesheuvel , Marc Zyngier , Alan Hayward , Christoffer Dall , linux-arch@vger.kernel.org, libc-alpha@sourceware.org, Florian Weimer , Joseph Myers , Szabolcs Nagy , Torvald Riegel , gdb@sourceware.org, Yao Qi Subject: [RFC PATCH 09/10] arm64/sve: Enable default vector length control via procfs Date: Thu, 12 Jan 2017 11:26:08 +0000 Message-Id: <1484220369-23970-10-git-send-email-Dave.Martin@arm.com> In-Reply-To: <1484220369-23970-1-git-send-email-Dave.Martin@arm.com> References: <1484220369-23970-1-git-send-email-Dave.Martin@arm.com> This patch makes the default SVE vector length at exec() for user tasks controllable via procfs, in /proc/cpu/sve_default_vector_length. Limited effort is made to return sensible errors when writing the procfs file, and anyway the value gets silently clamped to the maximum VL supported by the platform: users should close and reopen the file and read back to see the result. Signed-off-by: Dave Martin --- Caveats: * /proc may not be the correct place for this (but it's not clear where in sysfs it should go either, and it's a global control with no corresponding kobject) * There seems to be no suitable framework for writable controls of this sort in /proc (unlike debugfs or sysfs). So, I had to write a suspiciously large amount of code -- I may have missed an obvious trick :P arch/arm64/kernel/fpsimd.c | 160 ++++++++++++++++++++++++++++++++++++++++++++- 1 file changed, 158 insertions(+), 2 deletions(-) diff --git a/arch/arm64/kernel/fpsimd.c b/arch/arm64/kernel/fpsimd.c index f010a1c..3c0e08c 100644 --- a/arch/arm64/kernel/fpsimd.c +++ b/arch/arm64/kernel/fpsimd.c @@ -22,8 +22,12 @@ #include #include #include +#include #include +#include #include +#include +#include #include #include @@ -102,9 +106,132 @@ void do_fpsimd_acc(unsigned int esr, struct pt_regs *regs) /* Maximum supported vector length across all CPUs (initially poisoned) */ int sve_max_vl = -1; +/* Default VL for tasks that don't set it explicitly: */ +int sve_default_vl = -1; #ifdef CONFIG_ARM64_SVE +#ifdef CONFIG_PROC_FS + +struct default_vl_write_state { + bool invalid; + size_t len; + char buf[40]; /* enough for "0x" + 64-bit hex integer + NUL */ +}; + +static int sve_default_vl_show(struct seq_file *s, void *data) +{ + seq_printf(s, "%d\n", sve_default_vl); + return 0; +} + +static ssize_t sve_default_vl_write(struct file *f, const char __user *buf, + size_t size, loff_t *pos) +{ + struct default_vl_write_state *state = + ((struct seq_file *)f->private_data)->private; + long ret; + + if (!size) + return 0; + + if (*pos > sizeof(state->buf) || + size >= sizeof(state->buf) - *pos) { + ret = -ENOSPC; + goto error; + } + + ret = copy_from_user(state->buf + *pos, buf, size); + if (ret > 0) + ret = -EINVAL; + if (ret) + goto error; + + *pos += size; + if (*pos > state->len) + state->len = *pos; + + return size; + +error: + state->invalid = true; + return ret; +} + +static int sve_default_vl_release(struct inode *i, struct file *f) +{ + int ret = 0; + int t; + unsigned long value; + struct default_vl_write_state *state = + ((struct seq_file *)f->private_data)->private; + + if (!(f->f_mode & FMODE_WRITE)) + goto out; + + if (state->invalid) + goto out; + + if (state->len >= sizeof(state->buf)) { + WARN_ON(1); + state->len = sizeof(state->buf) - 1; + } + + state->buf[state->len] = '\0'; + t = kstrtoul(state->buf, 0, &value); + if (t) + ret = t; + + if (!sve_vl_valid(value)) + ret = -EINVAL; + + if (!sve_vl_valid(sve_max_vl)) { + WARN_ON(1); + ret = -EINVAL; + } + + if (value > sve_max_vl) + value = sve_max_vl; + + if (!ret) + sve_default_vl = value; + +out: + t = seq_release_private(i, f); + return ret ? ret : t; +} + +static int sve_default_vl_open(struct inode *i, struct file *f) +{ + struct default_vl_write_state *data = NULL; + int ret; + + if (f->f_mode & FMODE_WRITE) { + data = kzalloc(sizeof(*data), GFP_KERNEL); + if (!data) + return -ENOMEM; + + data->invalid = false; + data->len = 0; + } + + ret = single_open(f, sve_default_vl_show, data); + if (ret) + kfree(data); + + return ret; +} + +static const struct file_operations sve_default_vl_fops = { + .open = sve_default_vl_open, + .read = seq_read, + .llseek = seq_lseek, + .release = sve_default_vl_release, + .write = sve_default_vl_write, +}; + +#endif /* !CONFIG_PROC_FS */ + static void task_fpsimd_to_sve(struct task_struct *task); static void task_fpsimd_load(struct task_struct *task); static void task_fpsimd_save(struct task_struct *task); @@ -299,7 +426,7 @@ void fpsimd_flush_thread(void) !(current->thread.sve_flags & THREAD_VL_INHERIT)) { BUG_ON(!sve_vl_valid(sve_max_vl)); - current->thread.sve_vl = sve_max_vl; + current->thread.sve_vl = sve_default_vl; current->thread.sve_flags = 0; } } @@ -723,6 +850,14 @@ void __init fpsimd_init_task_struct_size(void) & 0xf) == 1) { /* FIXME: This should be the minimum across all CPUs */ sve_max_vl = sve_get_vl(); + sve_default_vl = sve_max_vl; + + /* + * To avoid enlarging the signal frame by default, clamp to + * 512 bits until/unless overridden by userspace: + */ + if (sve_default_vl > 512 / 8) + sve_default_vl = 512 / 8; arch_task_struct_size = sizeof(struct task_struct) + 35 * sve_max_vl; @@ -734,6 +869,27 @@ void __init fpsimd_init_task_struct_size(void) /* * FP/SIMD support code initialisation. */ +static int __init sve_procfs_init(void) +{ +#if defined(CONFIG_ARM64_SVE) && defined(CONFIG_PROC_FS) + struct proc_dir_entry *dir; + + if (!(elf_hwcap & HWCAP_SVE)) + return 0; + + /* This should be moved elsewhere is anything else ever uses it: */ + dir = proc_mkdir("cpu", NULL); + if (!dir) + return -ENOMEM; + + if (!proc_create("sve_default_vector_length", + S_IRUGO | S_IWUSR, dir, &sve_default_vl_fops)) + return -ENOMEM; +#endif + + return 0; +} + static int __init fpsimd_init(void) { if (elf_hwcap & HWCAP_FP) { @@ -749,6 +905,6 @@ static int __init fpsimd_init(void) if (!(elf_hwcap & HWCAP_SVE)) pr_info("Scalable Vector Extension available\n"); - return 0; + return sve_procfs_init(); } late_initcall(fpsimd_init);